The present invention relates generally to test fixtures and, more particularly, to test fixtures suitable for high speed automatic testing of planar electronic devices, including electronic assemblies in general and high density interconnect (HDI) modules having a plurality of contact pads.
For testing planar electronic devices such as HDI modules of the type described in Eichelberger et al. U.S. Pat. No. 4,783,695 issued Nov. 8, 1988 and assigned to the instant assignee, it is usual to employ high speed automatic test equipment (ATE) suitably connected to various inputs and outputs of a device under test (DUT). The automatic test equipment exercises the device under test by rapidly applying a series of test vectors to the device inputs, and checking for expected output signals. The automatic test equipment runs at high speed to minimize the time required for testing. Perhaps more significantly, for a complete test it is necessary to exercise the device at its intended operating frequency, which may be 50 MHz, or higher. In the case of a planar electronic device which is an HDI module, testing is performed prior to final packaging of the module. This is particularly significant in increasing yield, because an HDI module may readily be repaired in the event it fails a test.
A previous approach for testing HDI modules in particular involves using a fixture including a probe card holding spring-loaded "pogo" pins which make contact to test pads on the HDI modules. The "pogo" pin probe card in turn is connected to the automatic test equipment via a wire harness including individual wires or cables with or without standard interface connectors. Typically, the automatic test equipment employs a general purpose ATE load board, which is a carefully designed, multi-layer printed circuit board having well-controlled impedance characteristics. The load board mates directly with the automatic test equipment, and provides connection points for connection to a device under test through the cables.
With this previous approach, the long cable length adds too much loading for high speed testing. Also if the interconnect is not fully defined, appropriate connections to allow high speed testing cannot be made. Moreover, alignment of the test fixture to the HDI module is not easily accomplished because of the small (10 mil.times.10 mil) HDI pad size, and the large number of contact pads (as many as 276) around the periphery of a two inch by two inch module.
Moreover, in some circumstances, the spring-loaded "pogo" pin contacts can physically damage the device contact pads during testing.